The major objectives of the proposed studies are to examine what factors regulate the synthesis and secretion of lipoproteins in cultured rat hepatocytes. Hepatocytes obtained from male Sprague-Dawley rats will be cultured as monolayers on plastic petri dishes using methods which we have previously reported. Lipoproteins will be isolated, and the lipid composition will be quantitated. The apolipoproteins will be characterized by electrophoresis and isoelectric focusing, and quantitated by rocket immunoelectrophoresis. Synthesis of both the lipid and apolipoproteins will be determined by measuring the incorporation of labeled precursors into each component of the newly secreted lipoproteins. The major emphasis of the proposed research is to examine how different hormones: glucagon, insulin and estrogen and different nutrients: cholesterol, fatty acid, and carbohydrate, regulate lipoprotein synthesis and secretion. Hormones and nutrients will be added separately and in combination to the culture medium of hepatocytes, in order to mimic normal physiologic and pathophysiologic conditions characteristic of hypercholesterolemic and diabetic states. Data will be evaluated with respect to primary hormonal response and secondary effects. The results may aid our understanding of how hormones and nutrients regulate lipoprotein synthesis and how and/or why the regulation may be altered in diabetes mellitus and other conditions associated with disordered lipid metabolism.